569 FXUS65 KTFX 212331 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 530 PM MDT Sat Mar 21 2020 ...Update to Aviation... .SYNOPSIS... A cold front will advance south across the region this afternoon through the overnight hours tonight, bringing a shift in wind direction to the north and light accumulating snow. With road surfaces above freezing this afternoon, any that snow that falls initially will melt. Once roads have cooled late this evening, any wet roads could become slippery, especially where snow continues to fall. && .DISCUSSION... Rest of this afternoon through Sunday night...biggest concern over the period will be a passing cold front and upper level disturbance this afternoon through the overnight hours tonight, which will bring light snow accumulations to portions of Southwest through North Central Montana. Main message with regards to the snow this evening through tonight is not the amount of snow that will fall, but rather the fact that road surface will remain well above freezing with the initial onset of precipitation this evening. As of the is afternoon, road surfaces across the region ranged from the 50s to low 80s, with these surfaces not expected to fall below freezing until between 04z-08z Sunday. This means that any snow that falls before or during this timeframe will likely melt until road surfaces have cool to the freezing point. After road surfaces have cooled late this evening/early Sunday morning, icy conditions could develop, especially where snow continues to fall on the already saturated surfaces. It is therefore not the amount of snow that will cause the biggest impacts to travel through Sunday morning, but rather how quickly roadways freeze and how much additional snow falls on top of these slippery surfaces. As the upper level disturbance departs the region Sunday morning, expect surface winds to veer to the southwest and skies to clear. These southwest winds and clear skies will lead to another above/near normal day on Sunday across most of Southwest through North Central Montana, with the one exception being the Hi- Line where below temperatures are expected. - Moldan Monday through next Saturday...Temperatures are expected to rise well above normal for the day on Monday ahead of a strong upper level trough digging south into the Pacific Northwest. Most locations on Monday are expected to rise into the upper 40s to mid- 50s, before falling back into the 30s to mid-40s on Tuesday as a cold front advances south across the region. By Monday afternoon, moist southwest flow is expected to develop over the Northern Rockies, persisting through Tuesday night. This pattern will lead to numerous/widespread mountain snow/snow showers over the timeframe, with scattered precipitation (rain/snow) spreading east over the valleys/plains late Monday night through Wednesday morning. At this time, snowfall amounts over the plains and in the valleys of generally less than 2 inches are expected from Monday night through Wednesday morning, with up to 8 inches over most mountain passes. After a brief break from precipitation Wednesday night, unsettled northwest flow will develop across the region and lead to additional chances for precipitation through the end of the work week, especially in the mountains. - Moldan && .AVIATION... Updated 530 PM MDT Sat Mar 21 2020 (22/00Z TAF Period) Weak disturbance will bring increasing clouds this evening with snow showers developing across western portions of the forecast area by 06Z. VFR conditions expected to prevail early in the period but lowering clouds and areas/periods of snow will likely produce IFR/MVFR conditions with local LIFR ceilings at times. System will move eastward with skies clearing out for most of the forecast area before 00Z Monday. Mountains will be obscured tonight through late Sunday afternoon. mpj && .PRELIMINARY POINT TEMPS/POPS... GTF 22 46 31 55 / 70 10 0 0 CTB 17 41 29 49 / 40 0 0 0 HLN 26 52 29 55 / 50 30 0 10 BZN 25 47 26 52 / 40 40 0 0 WYS 19 38 19 39 / 30 20 10 10 DLN 27 46 26 49 / 20 20 0 0 HVR 19 40 23 51 / 20 0 0 0 LWT 21 40 27 50 / 70 30 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls